Dual-fuel engines will be essential to meet EEDI Phase 3 when it comes into force for tankers and bulk carriers, Rudolf Wettstein, general manager for marketing and application in WinGD’s sales and marketing team, suggested to The Motorship.
To meet that ambition with the equivalent diesel engine would require the ship’s designers to find additional solutions, such as reducing their ship’s power demand, optimising its auxiliary power generation – for example by using PTO arrangements – or applying other power-saving technologies.
Even battery hybrid installations could form part of future energy-saving initiatives on large bulk carriers and tankers, said Dr German Weisser, senior advisor emissions, research and development at the engine designer, who reported that the company is “investigating the possibilities of applying such concepts to a variety of different vessel types.”
Such installations are becoming common in smaller vessels with medium-speed main engines and Dr Weisser agreed that “bulkers and tankers may have less potential” than those to benefit from hybrid arrangements, “but ultimately, whatever helps, helps,” he said. The project’s initial focus is on smaller ships for which manoeuvring is a priority – such as mid size car carriers and chemical tankers rather than VLCCs – “but it can expand into that area,” Mr Wettstein said. Neither executive would speculate on a timetable for that development, however.
LNG carrier designers are also incorporating some innovative energy-saving features as a result of EEDI compliance. Unlike tankers and bulkers, LNG carriers will have to meet Phase 3 standards in 2022 and some are being fitted with energy-saving technologies in readiness.
Mr Wettstein mentioned two in particular, noting that some South Korean yards are offering air lubrication as an option for such ships, saying that their twin screw stern shape leads to them having wide and flat bottoms, which makes them particularly suited to benefit from that technology.
Some LNG carriers are also now being ordered with PTO power generation installations rather than auxiliary generators to take advantage of the main engine’s lower fuel consumption and reduce their EEDI. From an economic point of view, low-speed PTOs can be an expensive option, Mr Wettstein said, but “shipyards want to offer a drop in EEDI.”
Barred speed range
Concerns about operating low speed engines in their barred speed range – at which there is a risk of harmful torsional vibrations – is often raised in discussions about meeting EEDI by reducing speed, but WinGD believes there are simple ways to avoid the problem.
Mr Wettstein acknowledged that this has been a problem in the past, with some engines taking minutes to accelerate through that range, but now most shipyards have found they can tune a propulsion system so that its barred speed range is towards the low end of the speed range, allowing the engine to accelerate through it in about 20 seconds.
In fact, the problem may be eliminated altogether by arranging the right combination of mass moment of inertia on the propeller and propeller shaft, along with tuning the flywheel and perhaps adding a torsional vibration damper, he added.
That is not to say that engine designers have not contributed anything to this achievement. “We have raised our overload limits slightly to make a bigger reserve [in the low speed range],” he said, but it is its engine builders that carry out the torsional vibration calculations and liaise with shipyards to implement their recommendations.
EEDI has had its day
EEDI is “coming to the end of its useful lifetime,” believes German Weisser, senior advisor emissions, research and development at enginebuilder WinGD. Stressing that his remarks reflected only his personal view, he said that IMO should instead devote more time to its broader strategy to reduce greenhouse gases (GHGs), he told The Motorship.
In its initial phase, EEDI had been valuable in creating awareness in the industry about energy efficiency and its impact on addressing GHG emissions, he said, but now “it is my firm opinion that … we need to focus more on those aspects that bring larger contributions” to tackling concerns about GHG “and move away from looking into design criteria, which we cannot expect to contribute significantly anymore.”
One specific concern he mentioned is that “any impact of alternative fuels cannot be modelled into an EEDI concept very clearly.” Although the index includes a factor related to fuel type – for LNG the figure is 2.75 and for diesel fuel it is 3.1 – Dr Weisser said that if a ship were to use synthetic methane, “you cannot show this in its EEDI or EEXI because your engine can always run either on the fossil fuel or on the renewable fuel.”
The only way for renewable fuels to be reflected in a ship’s EEDI would be to design it to use a particular renewable fuel exclusively, with no ability to run on a backup fuel when the renewable fuel is not available. “I don’t think that we’re going to see this until renewable fuels become available worldwide in abundant quantities,” he said.
Instead of EEDI, he would prefer to see an operational parameter used, such as IMO’s voluntary Energy Efficiency Operational Index (EEOI).
He is not alone in supporting EEOI; in its latest annual sustainability report, published earlier this year, the major tanker operator AP Moller Maersk reported that in 2019 it had begun using EEOI as its preferred indicator to track its CO₂ reduction target. By using an indicator “based on our actual operational performance, the result is more accurate data”, its report says. Because of this policy, it has restated its data going back to 2008 and suggests that EEOI “become[s] the indicator to be used to measure progress on the IMO efficiency targets.”